正交分頻多工(OFDMA)被視為未來第四代無線通訊系統的一種調變和多工存取的技術。OFDMA是從OFDM衍伸出來的存取技術，它與OFDM的不同處在於，它讓多個使用者在相同訊號傳遞時間內，可以使用不同的子載波作傳送。本篇論文主要是對資源分配的問題，在有傳輸功率和使用者資料傳輸速率的限制下，做適當的子載波分配。這邊我們提出三個步驟來解決這個問題：調變的判定，符合使用者的服務品質，允入控制。主要的目摽是在有滿足每個使用者的服務品質下，可以提高整體的資源使用率。根據使用者的所在位置，我們可以選擇適當的調變技術。當使用者在移動的時候，會因為督普勒效應而產生頻率偏移，頻率偏移就會造成子載波之間失去它的正交性，所以，我們提出一種子載波分配的方法去緩和子載波間的干擾。從模擬結果看到，我們提出的子載波分配的方法可以比其他方法更能緩和子載波間的干擾，而且整體的平均傳送功率會降低。 OFDMA is being considered as a modulation and multiple access method for 4th generation wireless networks. Orthogonal Frequency Division Multiple Access (OFDMA) basestations allow multiple users to transmit simultaneously on different subcarriers during the same symbol period. This thesis considers the resource allocation problem of assigning a set of subcarriers, subject to constraints on users’ required data rate and transmits power. We solve the problem via three steps: modulation determined, meet the users’ required data rate, admission control. The objective is to maximize the resource utilization in a network, while a required Quality of Service (QoS) per user is satisfied. According to the users’ position, we can apply it to the suitable modulation. When users are moving, the frequency spread caused by Doppler effects will destroy the orthogonality between subcarriers. So, we proposed a subcarrier allocation scheme to minimize the inter-carrier interference (ICI). Results show that the inter-carrier interference will be mitigated than other subcarrier allocation and the total transmission power will be decreased.
